An X-ray CT apparatus is for obtaining a tomogram of an object by irradiating X-ray from an X-ray tube to the object while rotating the X-ray tube around the object, detecting projection data from various angle directions around the object by an X-ray detector, and performing image reconstruction calculation on the detected projection data.
In X-ray CT apparatus, there are occasions that the object moves while collecting projection data since the X-ray tube rotates around the object 180-360 degrees upon collecting projection data necessary for image reconstruction calculation. When the object moves, movement artifacts are generated which hinder the tomogram from being accurately reconstructed.
Since movement artifacts are notably generated especially upon setting a moving organ such as a heart that constantly repeats motion of expansion and contraction as the measurement region and they tend to be an obstacle to obtain the tomogram for diagnosis, various methods have been studied for the purpose of reducing them.
A technique to avoid movement artifacts is disclosed in Patent Document 1 as an example.
In this Document, a technique is described for reducing movement artifacts by applying ECG gate scan to a spiral scan, and interpolating discontinuity of projection data generated thereupon using, for example, data of heartbeat time phase in 180 degrees opposite relationship.
Patent Document 1: JP-A-2002-330961
However, there is a fear that the tomogram obtained by the previously mentioned method results in low quality, since the projection data used for this method was acquired in shorter time period compared to normal examination and the reconstruction of the tomogram is performed using the opposed beam data thereof, and therefore noise components are increased in the reconstructed tomogram. In other words, disclosed contents of Patent Document 1 cannot meet the needs for avoiding quality deterioration of the obtained tomogram.
Another method for preventing the above-mentioned influence to the image quality is to raise the energy of X-ray to a greater level than used in normal examination, but this will expose the object to more exposure to radiation. This method has no consideration for protecting the object from exposure to radiation.